Purifying gases



H. s. cooKE PURIFYING GASES Yeh. 20, 1940.

Original Filed Feb. 12, 1936 BCO:

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` FUR/HER COOLFB YfNT ACTIF/ER FGULD SOLUTION #cd/sumaron CCI/NUL i T0@ lNVENTOR HORACE B. COM

ATTO RNEY Reissued Feb. 20, 1940 UNITED STATES PATENT OFFICE Process Management Company,

Inc., New

York, N. Y., a corporation of Delaware Original No. 2,134,507, dated October 25, 1938,

Serial No. 63,493, February 12, 1936. Application for reissue April 22, 1939, Serial 2 Claims.

This invention relates to a method o1' purifying gases and pertains more particularly to an improved method for removing hydrogen sulphide from gases by means of an alkaline solution such as sodium carbonate.

While my invention will have more general application, it is of special advantage in the purification of renery gases resulting from the cracking of hydrocarbon oil; and wherein the puried gases are subjected to further processing for the formation of valuable products therefrom. Until recently these gases have been largely waste products and used as fuel in the oil-refining process and elsewhere. Under more modern practice, these gases, which contain a relatively large proportion of unsaturated hydrocarbons, have been subjected to polymerization treatment to produce liquid polymers Within a motor-fuel boiling range and having exceptionally high antiknock characteristics. The presence of hydrogen sulphide in the refinery gases delivered to the polymerization operation is objectionable for a number of reasons. It tends to cause corrosion of apparatus, imparts a disagreeable odor to the iinshed products, and may adversely alect the polymerization reaction, particularly when catalysts are employed. Moreover, the hydrogen sulphide may react with the hydrocarbons undergoing treatment, thereby resulting in a final product difcult or impossible to refine by ordinary methods.

It has heretofore been proposed to remove hydrogen sulphide from gases by contacting the same with an aqueous alkaline solution, such as a dilute solution of sodium carbonate. The primary reaction may be expressed as follows:

The spent alkaline solution is then reactied by subjecting the spent solution to conditions conducive to reversing the reaction as follows:

In practice this is usually accomplished by blowing the solution with air or other inert gas. In such operations the amount of air required in the reactivation may be from two to three times the amount of gas purified.

Various other methods of actfying foul solutions of this character have been suggested, but are open to various disadvantages. Vacuum actication is expensive, and has not, so far as I know, been successful in this country. Simple alkaline solutions are not, under ordinary conditions, suitable for actication by heating, on

account of the relatively low carrying capacity of such solutions for hydrogen sulphide. On the other hand, gas-purifying solutions, such as a solution of sodium phenolate, which are suitable for actication by heat, cannot be used for the purification of hydrocarbons in the liquid phase.

A principal object of my invention is to provide an improved process which will require equipment of smaller capacity per unit volume of gases treated, which will reduce the amount of alkaline solution necessary per unit volume of gases treated and wherein the actiiication or reactivation may be accomplished in a simpler and more economical manner.

Other and more detailed objects and advantages of my invention Will be apparent from a more detailed description hereinafter.

In accordance with my invention, the hydrocarbon gas to be puried of hydrogen sulphide, such as refinery gas, or refinery gas which has been largely freed from hydrogen or methane by any of the old and well known methods, or other hydrocarbon gas largely composed of hydrocarbons hav-ing from two to four carbon atoms per molecule, while at a temperature at or below the critical thereof, is subjected to a pressure adequate to convert it into a liquid. This liquid is then contacted with a dilute sodium corbonate solution containing for example from l to 6% of sodium carbonate. Since the hydrogen sulphide is in liquid phase and is consequently more highly concentrated than it would be in vapor phase, the reaction velocity of the first named reaction and the proportion of sodium hydrosulphide resulting therefrom is increased. While the iirst reaction is believed to be the primary one taking place in the purifying zone, other reactions tending to increase the amount of hydrogen sulphide absorbed by the solution may take place. In any event, the amount of hydrogen sulphide absorbed by a given volume of alkaline solution is higher when the reaction is accomplished under the pressure required to maintain the hydrocarbons in liquid phase.

After contact with the hydrocarbons, the spent alkaline solution is separated from the purified liquid and actied under lower pressure, for example, at atmospheric pressure. Under the reduced pressure the concentration of hydrogen sulphide gas will be reduced, thus reversing the reaction and effecting a removal of the absorbed hydrogen sulphide. Additional hydrogen sulphide removal may be accomplished by subjecting the solution to heat or by blowing with air, steam, or other inert gas. During the removal of the hydrogen sulphide in the actication zone carbon dioxide may be released and where this occurs, the solution should be replenished in CO2 somewhere in the cycle in order to maintain the sodium carbonate solution at the desired strength. The rea-ctied alkaline solution is then returned to the system.

With the above general nature and principal objects in view, the invention will be better understood from the more detailed description hereinafter, in which reference will be made to the accompanying drawing forming a part of this description.

Referring to the drawing, the reference character I@ designates a charging line for receiving the gases to be treated to remove hydrogen sulphide therefrom. These gases are freed of hydrogen and methane prior to entering line It and a well known manner for removing the hydrogen and methane will oe briefly described although any other conventional method may be employed. Hydrocarbon gases, such as renery gases, are conducted through line I having a compressor 2 to a iractionating tower 3 having suitable plates or fractionating trays Il. The fractionating tower 3 is maintained at a sufficiently low temperature and et a suiiiciently high pressure to eiect separation of the hydrogen and methane in gaseous condition from hydrocarbon gas largely composed of constituents having from two to four carbon atoms per molecule in liqueed condition. The hydrogen and methane in gaseous condition are removed from the fractionating tower 3 through line 5 having a valve E and the liquefied hydrocarbons or" lfrom two to four carbon atoms per molecule collect in the lower portion of the tower 3. These liquefied hydrocarbons are withdrawn from tower 3 through line 'l and are passed to a suitable accumulator 8. The normally gaseous hydrocarbons from accumulator 8 are conducted through line 9 to charging line IU. The charging line lil is provided with a compressor pump l! for compressing the gas below the vaporization pressure thereof. The pressure required will depend upon the nature of the gas and may range i'rom 2GB to 1200 or more pounds per square inch. In case of renery gas a pressure between 309 and 600 pounds per square inch is usually adequate.

The pressure side of compressor pump II discharges through line l2 which terminates in a nozzle ring i3 located near the bottom of the absorption tower I, from whence the liquefied gas passes upwardly through the tower countercurrent to a flow of alkaline solution introduced into the top of the tower through nozzle I5. The invention preferably contemplates the use of dilute solution of sodium carbonate containing from l to 6% sodium carbonate although other weak alkaline solutions may be employed.

The flow of liquefied gas and alkaline solution is regulated to give the desired purifying elect. The tower ld may, as shown, contain solid contact or packing material Il, for example loosely spaced brick located on spaced trays within the tower.

Preferably the rings I3 and I5 are sufliciently spaced from the ends oi the tower I to provide for separating zones below and above the same, respectively.

The purified, liquefied gas is withdrawn from the top ol tower I4 through line I3 and may be passed to storage tanks not shown) or directly to further processing equipment such as a polymerization unit. The fouled alkaline solution is withdrawn from the bottom of tower I4 through line I9 provided with reducing valve 20 and discharges under reduced pressure into the top of actifying tower 2l. The actifying tower 2| preferably contains solid contact material, which may be in the form of loose brick 23 disposed on spaced perforated trays 24.

Air or other inert gas may be passed into the tower 2i through line 26 and blown upwardly through the tower by means of blower 21 countercurrent to the flow of the alkaline solution.

The actied solution is withdrawn from the bottom of the actifying tower 2l through line 28 and passed to an accumulating tank 29 from which it may be withdrawn through line 30 and forced by means of a pump 3I to a cooler 32 and thence to the spray nozzle I5 in the purifying tower M and recycled through the system. The hydrocarbons undergoing treatment and the purifying solution in the tower I4 are preferably maintained at atmospheric temperature or thereabout.

The hydrogen sulphide liberated, combined with inert gas introduced in the bottom of the tower ZI, in case such gas is introduced, is removed from actifying tower 2i through a vent pipe 33. Carbon dioxide to replenish that removed in the actifying tower, or steam, may be introduced into the bottom of the tower through a line 34. An indirect heating coil 35 may be provided as shown in the bottom of the tower 2|.

If desired carbon dioxide for replenishing the solution may be introduced into the relatively cooler reactifled solution on the high pressure side of the cycle through line 3B beyond the cooling coil 32.

The operability of the process is made possible by relative reaction velocities of the following reversible reaction under different temperature and pressure conditions:

NazCOa -I-HzSNaHS-l-NaI-ICOs By liquefying the gases to be treated the concentration of the hydrogen sulphide in the purifier is increased, thus shifting the reaction. equilibrium to the right to form a relatively larger proportion of sodium hydrosulphide, and by reducing the pressure in the actifier substantially below that existing in the purier and below the vaporizing pressure of hydrogen sulphide the reaction equilibrium is shifted back to the left, thus releasing the hydrogen sulphide as a gas. It will be observed that according to my process, liquid phase conditions prevail in the purifier, whereas in the actiiier the hydrogen sulphide is in vapor phase and is removed from the system as formed.

It will be understood that fresh solution should be added to the system continuously or from time to time to maintain the desired strength and to replace that lost by unfavorable side reactions.

Having described the preferred embodiment, it is understood that my invention embraces such other modifications and variations as come within the spirit and scope thereof and that it is not my intention to unduly limit the invention or dedicate any novel features thereof.

I claim:

1. A method of desulphurizing gases obtained from oil refinery operations which comprises separating hydrogen and methane from said gases to obtain normally gaseous hydrocarbons containing at least two carbon atoms per molecule therefrom, passing said normally gaseous hydrocarbons through a treating zone at a temperature suiiiciently low and at a pressure surlicient- 75 ly high to maintain said gases in liquefied condition, intimately contacting said gases While in liquefied state in said treating zone with a sodium carbonate solution capable of reacting With sulphur-containing compounds in said liquefied gas, separating the thus treated lique- Iied hydrocarbons from the sodium carbonate solution containing the sulphur compounds, passing the sodium carbonate solution containing the sulphur compounds to an activation zone and therein treating it to remove sulphur compounds at a lower pressure than that in said treating zone but not lower than atmospheric pressure to facilitate removal of sulphur compounds from the sodium carbonate solution and to reactivate the sodium carbonate solution for further use and returning the reactivated sodium carbonate solution thus obtained to said treating zone.

2. A method of desulphurizing gases obtained from oil renery operations which comprises separating hydrogen and methane from said gases to obtain normally gaseous hydrocarbons containing at least two carbon atoms per molecule therefrom, passing said normally gaseous hydrocarbons through a treating zone at a temperature sufficiently low and at a pressure suiciently high to maintain said gases in liquefied condition, intimately contacting said gases While in liquefied state in said treating Zone with a sodium carbonate solution capable of reacting With sulphur-containing compounds in said liqueed gas, separating the thus treated liqueed hydrocarbons from the sodium carbonate solution containing the sulphur compounds, passing the sodium carbonate solution containing the sulphur compounds to an activation zone maintained under a lower pressure than that in said treating sone but not lower than atmospheric to facilitate removal of sulphur compounds and heating the sodium carbonate solution containing the sulphur compounds in said activation zone to reactivate the sodium carbonate solution for further use and returning the reactivated sodium carbonate solution thus obtained to said treating zone.

HORACE B. COOKE. 

